Grow Your Own Groovy Green Roof

Photograph of a hydroponic green roof made of sponges with green sprouts on top.

Did you know you can grow plants without soil? Hydroponics uses water and a growth medium to grow plants. NASA has been researching how to use hydroponics in space. The theme for our October subscription box, Water Works, is about how a future Mars Colony could grow their own food hydroponically. This investigation is all about making your own space barn with a green roof and learning how seeds can grow with only a sponge and some water.


  • 2 Compressed rectangle sponges
  • Seeds – Alfalfa, Chia or Wheatgrass
  • Pipette
  • Toothpicks
  • Large poly (plastic) bag
  • Rubber band
  • 3 Straws
  • Groovy space plate (plastic plate)
  • Scissors
  • Permanent marker 

Space Barn: Roof

1.    Place one sponge on a flat surface.   Measure the length of the sponge.  To calculate half the length of your sponge, divide the number you measure by 2.

Example: If the length of a sponge is 12 cm…

12 cm ÷ 2 = 6 cm 

…then half the length of a sponge is 6 cm.  

2.   Measure and mark two dots at the halfway points, then draw a line connecting the two points. 

Illustration of a sponge with a cut line at the halfway mark.

3.   Cut along the straight line so you have two thin rectangles which will be used for your space barn roof in a few more steps. 

Space Barn: Front Door & Back Wall

4.   Place the second sponge on a flat surface. From the top left corner measure and mark 5.5 cm along the left and top sides. 

5.   Then, draw a line connecting the two points. 

6.   From the bottom right corner measure and mark 5.5 cm along the right and bottom sides. 

7.    Then draw a line connecting the two points.  

Illustration of a sponge showing cut marks on the corners.

8.   Cut the rectangular sponge along the two straight lines.

Space Barn: Front Door

9.   With one triangle sponge oriented with the 90-degree angle at the top left corner, measure and mark 1 cm points along the left and top edges of the sponge.

10.  Draw a line connecting the 1 cm points to make a mini-triangle.  Cut along the line, then put the mini triangle to the side. 

Illustration that shows front and back walls of the space barn.

11.   Place your compressed sponges under running water and allow them to fully expand.  Remove your sponges from the water and wring them so they are damp. You want the sponge to be damp, but not dripping.

Photograph of a little girl putting sponges into water.

GROOVY GROWN-UP HELP:  You will be using toothpicks as pegs to hold your space barn together.  Take a toothpick and rotate it clockwise in and out of the expanded sponges so you get the feel of how a toothpick will go through a sponge.  A toothpick will screw through a sponge more easily when you rotate the toothpick clockwise, instead of stabbing it through. 

Illustration that shows how to twist a toothpick into the sponge to push it through.

12.  Align four toothpicks so they peg through Sponge Roof 1 and are centered along the sides of the sponges Front Door and Back Wall.   

Illustrations that show how to attached the sides of the space barn's green roof to the front and back using toothpicks.

13.  Pinch your fingers around the toothpicks where you want to break the toothpick along the surface of the sponge.  

14.  Then SNAP forward (away from you), and SNAP backward (towards you). 

Illustration that shows hands snapping a toothpick.
Illustration that shows hands snapping a toothpick.

15.  Position the second sponge roof, Sponge Roof 2, so it stands vertically on its side while Sponge Roof 1 lies horizontally on a flat surface. 

16.  Align four toothpicks so they peg through Sponge Roof 2 and are centered along the sides of the sponges Front Door and Back Wall.  

Illustrations that show how to finish putting together your space barn.

GROOVY ALERT:  Now that your space barn is built, you can add color with permanent markers and make it your own.

17.  Place your space barn on a groovy space plate.  Add water to the top of your space barn using a pipette or straw.  You want the sponge that will become the green roof to be damp, but not dripping.  

18.  Take some seeds in your hand and sprinkle them over the roof of your space barn.  Any crevices (holes in the sponge) are great places for your seeds to burrow inside and begin to SPROUT which will make your green roof!

Photograph of little hands sprinkling seeds on the space barn to create a green roof.

Space Barn: Groovy Triangle Dome

19.  Place three straws parallel to each other, then wrap a rubber band approximately 4 cm from the top of the three straws.

20.  Place the banded straws in the corner of your large poly bag.  

21.  Then, pull the poly bag to the bottom of the straws and cut the bag about 1 cm below the straws.

22.  Cut the top corner of your poly bag just enough so the three straws fit through the hole tightly.  

23.  Place your groovy triangle dome on top of your space barn by spreading out the three legs around the perimeter of your space barn. Your triangle dome will limit the amount of water lost during evaporation yet allow your seeds to receive needed air circulation to create the green roof.   

Illustration showing completed green roof on a space barn covered to contain the moisture.

24.  Place your space barn near a window. You want your seeds to get lots of sunshine but no direct sunlight.

Sponges put together to create a space barn with seeds showing on top that will sprout to create a green roof.

Water Works” Groovy Lab in a Box

Hydroponic farms and gardens are the way of the future. You and your STEMists can learn more about hydroponic systems with the educational STEM activities found in the “Water Works” groovy box — explore different types of hydroponic systems, seed germination and photosynthesis! Build a water reservoir, test tube bean stalk, hanging raised beds, a groovy space barn and much, much, more! Practice essential 21st century science skills – pipetting, measuring volume and length, making observations and collecting data – aligned with the Next Generation Science Standards.

Join Now! and challenge your STEMists to a monthly Groovy Lab in a Box, full of everything a child needs to learn about and do hands-on science, technology, engineering, and mathematics (STEM) investigations. Our monthly box activates thinking, questioning, inquiring and original creation as we guide children through scientific inquiry and engineering design process.

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